Thank you for the compliment. I wrote the beginning of it (B&W graphics (QuickDraw), filesystem, port to Sun3/60, port to NeXT), although people smarter than I did some of the heavy lifting (port to DOS, port to Windows, color graphics (QuickDraw), synthetic CPU.
What an amazing project! It seems almost like a path to madness, trying to reverse engineer the platform, but there were applications even very early on that were mac only that were desirable on PCs.
Executor used some fiendishly clever tricks to achieve performance on 1990s hardware at the expense of portability (e.g. the possibility of 64-bit support). Advanced Mac Substitute has different priorities and doesn't use any code from Executor.
However, ROMLib looks like a good source of unofficial system documentation, which I expect I'll be consulting in the future as I work on parts where Apple's docs become less detailed.